There is a growing body of clinical information suggesting that massive transfusions can be associated with pulmonary failure in post operative patients. Optical detectors will be developed to detect and/or monitor platelet aggregates introduced into the circulatory system by high volume blood transfusion. The proposed technique involves the analysis of the spectrum of the fluctuations in the specific intensity scattered from platelet aggregates in whole blood. Two detectors would be developed: 1. An in-vitro aggregate detector which could be placed on the downstream side of the blood transfusion filter to detect size and number density of platelet aggregates introduced into the human circulatory system. This detector would be the prototype for an in-vitro aggregate detector. 2. An in-vitro aggregate detector compatible with existing fiberoptic oximetry systems would be developed which could detect size and number density of platelet aggregates within the human circulatory system. The advantages of these detectors will be their ability to detect platelet aggregates in unlysed, undiluted whole human blood.